Part 3

The next subject is, THE CURIOUS FORMATION OF THE EYE.--The _Eye_ infinitely surpasses all the works of man's industry. Its structure is one of the most wonderful things the human understanding can become acquainted with; the most skilful artist cannot devise any machine of this kind which is not infinitely inferior to the eye; whatever ability, industry, and attention he may devote to it, he will not be able to produce a work that does not abound with the imperfections incident to the works of men. It is true, we cannot perfectly become acquainted with all the art the Divine Wisdom has displayed in the structure of this beautiful organ; but the little that we know suffices to convince us of the admirable intelligence, goodness, and power of the Creator. In the first place, how fine is the disposition of the exterior parts of the eye, how admirably it is defended! Placed in durable orbits of bone, at a certain depth in the skull, they cannot easily suffer any injury; the over-arching eye-brows contribute much to the beauty and preservation of this exquisite organ; and the eye-lids more immediately shelter it from the glare of light, and other things which might be prejudicial; inserted in these are the eye-lashes, which also much contribute to the above effect, and also prevent small particles of dust, and other substances, striking against the eye.[2] The internal structure is still more admirable. The globe of the eye is composed of tunics, humours, muscles, and vessels; the coats are the cornea, or exterior membrane, which is transparent anteriorly, and opake posteriorly; the charoid, which is extremely vascular; the uvea, with the iris, which being of various colours, gives the appearance of differently coloured eyes; and being perforated, with the power of contraction and dilatation, forms the pupil; and, lastly, the retina, being a fine expansion of the optic nerve, upon it the impressions of objects are made. The humours are the aqueous, lying in the forepart of the globe, immediately under the cornea; it is thin, liquid, and transparent; the crystalline, which lies next to the aqueous, behind the uvea, opposite to the pupil, it is the least of the humours, of great solidity, and on both sides convex; the vitreous, resembling the white of an egg, fills all the hind part of the cavity of the globe, and gives the spherical figure to the eye. The muscles of the eye are six, and by the excellence of their arrangement it is enabled to move in all directions. Vision is performed by the rays of light falling on the pellucid and convex cornea of the eye, by the density and convexity of which they are united into a focus, which passes the aqueous humours, and pupil of the eye, to be more condensed by the crystalline lens. The rays of light thus concentrated, penetrate the vitreous humour, and stimulate the retina upon which the images of objects, painted in an inverse direction, are represented to the mind through the medium of the optic nerves.

The _visual orbs_ Remark, how aptly station'd for their task; Rais'd to th' imperial head's high citadel, A wide extended prospect to command. See the arch'd outworks of impending lids, With hairs, as palisadoes fenc'd around To _ward annoyance_ from without. _Bally._

Again:--

Who form'd the curious organ of the _eye_, And cloth'd it with its various tunicles, Of texture exquisite; with crystal juice Supply'd it, to transmit the rays of light; Then plac'd it in its station eminent, Well _fenc'd_ and _guarded_, as a _centinel_ To watch abroad, and needful caution give? _Needler._

The next subject is, THE CURIOUS STRUCTURE OF THE EAR.

The channel'd ear, with many a winding maze, How artfully perplex'd, to catch the sound. And from her repercussive caves augment! _Bally._

Dark night, that from the eye his function takes, The ear more quick of apprehension makes; Wherein it doth impair the seeing sense, It pays the HEARING--_double recompense_. _Shakspeare._

Although the ear, with regard to beauty, yields to the eye, its conformation is not less perfect, nor less worthy of the Creator. The position of the ear bespeaks much wisdom; for it is placed in the most convenient part of the body, near to the brain, the common seat of all the senses. The exterior form of the ear merits considerable attention; its substance is between the flexible softness of flesh, and the firmness of bone, which prevents the inconvenience that must arise from its being either entirely muscular or wholly formed of solid bone. It is therefore cartilaginous, possessing firmness, folds, and smoothness, so adapted as to reflect sound; for the chief use of the external part is to collect the vibrations of the air, and transmit them to the orifice of the ear. The internal structure of this organ is still more remarkable. Within the cavity of the ear is an opening, called the meatus auditorius, or auditory canal, the entrance to which is defended by small hairs, which prevent insects and small particles of extraneous matter penetrating into it; for which purpose there is also secreted a bitter ceruminous matter, called ear-wax. The auditory canal is terminated obliquely by a membrane, generally known by the name of drum, which instrument it in some degree resembles; for within the cavity of the auditory canal is a kind of bony ring, over which the membrana tympani is stretched. In contact with this membrane, on the inner side, is a small bone (malleus) against which it strikes when agitated by the vibrations of sound. Connected with these are two small muscles: one, by stretching the membrane, adapts it to be more easily acted upon by soft and low sounds; the other, by relaxing, prepares it for those which are very loud. Besides the malleus, there are some other very small and remarkable bones, called incus, or the anvil, as orbiculare, or orbicular bone, and the stapes, or stirrup: their use is, to assist in conveying the sounds received upon the membrana tympani. Behind the cavity of the drum, is an opening, called the Eustachian tube, which begins at the back part of the mouth with an orifice, which diminishes in size as the tube passes towards the ear, where it becomes bony; by this means, sounds may be conveyed to the ear through the mouth, and it facilitates the vibrations of the membrane by the admission of air. We may next observe the cochlea, which somewhat resembles the shell of a snail, whence its name; its cavity winds in a spiral direction, and is divided into two by a thin spiral lamina: and lastly is the auditory nerve, which terminates in the brain. The faculty of hearing is worthy of the utmost admiration and attention: by putting in motion a very small portion of air, without even being conscious of its moving, we have the power of communicating to each other our thoughts, desires, and conceptions. But to render the action of air in the propagation of sound more intelligible, we must recollect that the air is not a solid, but a fluid body. Throw a stone into a smooth stream of water, and there will take place undulations, which will be extended more or less according to the degree of force with which the stone was impelled. Conceive then, that when a word is uttered in the air, a similar effect takes place in that element, as is produced by the stone in the water. During the action of speaking, the air is expelled from the mouth with more or less force; this communicates to the external air which it meets, an undulatory motion; and these undulations of the air entering the cavity of the ear, the external parts of which are peculiarly adapted to receive them, strike upon the membrane, or drum, by which means it is shaken, and receives a trembling motion: the vibration is communicated to the malleus, the bone immediately in contact with the membrane, and from it to the other bones; the last of which, the stapes or stirrup, adhering to the fenestra ovalis, or oval orifice, causes it to vibrate; the trembling of which is communicated to a portion of water contained in the cavity called the vestibulum, and in the semicircular canals, causing a gentle tremor in the nervous expansion contained therein, which is transmitted to the brain; and the mind is thus informed of the presence of sound, and feels a sensation proportioned to the force or to the weakness of the impression that is made. Let us rejoice that we possess the faculty of hearing; for without it, our state would be most wretched and deplorable; in some respects, more sorrowful than the loss of sight; had we been born deaf, we could not have acquired knowledge sufficient to enable us to pursue any art or science. Let us never behold those who have the misfortune to be deaf, without endeavoring better to estimate the gift of which they are deprived, and which we enjoy; or without praising the goodness of God, which has granted it to us: and the best way we can testify our gratitude is, to make a proper use of this important blessing.

We now proceed to a more particular description of THE CURIOSITIES OF THE HUMAN HEART; AND THE CIRCULATION OF THE BLOOD.

Though no shining sun, nor twinkling star Bedeck'd the crimson curtains of the sky; Though neither vegetable, beast, nor bird, Were extant on the surface of this ball, Nor lurking gem beneath; though the great sea Slept in profound stagnation, and the air Had left no thunder to pronounce its Maker: Yet Man at home, _within himself_ might find The Deity immense, and in that frame _So fearfully, so wonderfully made_! See and adore his providence and power. _Smart._

With what admirable skill and inimitable structure is formed that muscular body, situated within the cavity of the chest, and called the human heart! Its figure is somewhat conical, and it is externally divided into two parts: the base, which is uppermost, and attached to vessels; and the apex, which is loose and pointing to the left side, against which it seems to beat. Its substance is muscular, being composed of fleshy fibres, interwoven with each other. It is divided internally into cavities, called auricles and ventricles; from which vessels proceed to convey the blood to the different parts of the body. The ventricles are situated in the substance of the heart, and are separated from each other by a thick muscular substance; they are divided into right and left, and each communicates with its adjoining auricle, one of which is situated on each side the base of the heart. The right auricle receives the blood from the head and superior parts of the body, by means of a large vein; and in the same manner the blood is returned to it from the inferior parts, by all the veins emptying their stores into one, which terminates in this cavity; which, having received a sufficient portion of blood, contracts, and by this motion empties itself into the right ventricle, which also contracting, propels the blood into an artery, which immediately conveys it into the lungs, where it undergoes certain changes, and then passes through veins into the left auricle of the heart, thence into the left ventricle, by the contraction of which it is forced into an artery, through whose ramifications it is dispersed to all parts of the body, from which it is again returned to the right auricle; thus keeping up a perpetual circulation, for, whilst life remains, the action of the heart never ceases. In a state of health the heart contracts about seventy times in a minute, and is supposed, at each contraction, to propel about two ounces of blood; to do which, the force it exerts is very considerable, though neither the quantity of force exerted, nor of blood propelled, is accurately determined. The heart comprises within itself a world of wonders, and whilst we admire its admirable structure and properties, we are naturally led to consider the wisdom and power of Him who formed it, from whom first proceeded the circulation of the blood, and the pulsations of the heart; who commands it to be still, and the functions instantly cease to act.

This important secret of the circulation of blood in the human body was brought to light by William Harvey, an English physician, a little before the year 1600: and when it is considered thoroughly, it will appear to be one of the most stupendous works of OMNIPOTENCE.

_The blood_, the fountain whence the spirits flow, The generous stream that waters every part, And motion, vigour, and warm life conveys To every particle that moves or lives, ----------------through unnumber'd tube. _Pour'd by the heart_, and _to the heart again Refunded_.---------- _Armstrong._

Who in the dark the vital flame illum'd, And from th' impulsive engine caused to flow Th' ejaculated streams through many a pipe _Arterial_ with meand'ring lapse, then bring Refluent their _purple tribute_ to their fount: Who spun the _sinews'_ branchy thread, and twin'd The azure _veins_ in spiral knots, to waft Life's tepid waves all o'er; or, who with _bones_ Compacted, and with nerves the fabric strung: Their specious form, their fitness, which results From figure and arrangement, all declare Th' Artificer Divine! _Bally._

Again:--

The nerves, with equal wisdom made. Arising from the tender brain, pervade And secret pass in pairs the channel'd bone. And thence advance through paths and roads unknown. Form'd of the finest complicated thread, The num'rous cords are through the body spread. These subtle channels, such is every nerve, For vital functions, sense, and motion serve;-- They help to labour and concoct the _food_, Refine the _chyle_, and animate the _blood_. _Blackmore._

We now proceed to some CURIOUS AND INTERESTING FACTS CONCERNING RESPIRATION, OR THE ACT OF BREATHING.

Anatomists have, not unaptly, compared the lungs to a sponge; containing, like it, a great number of small cavities, and being also capable of considerable compression and expansion. The air cells of the lungs open into the windpipe, by which they communicate with the external atmosphere: the whole internal structure of the lungs is lined by a transparent membrane, estimated by Haller at only the thousandth part of an inch in thickness; but whose surface, from its various convolutions, measures fifteen square feet, which is equal to the external surface of the body. On this extensive and thin membrane innumerable branches of veins and arteries are distributed, some of them finer than hairs; and through these vessels all the blood in the system is successively propelled, by an extremely curious and beautiful mechanism, which will be described in some future article.

The capacity of the lungs varies considerably in different individuals.[3] On a general average, they may be said to contain about 280 cubic inches, or nearly five quarts of air. By each inspiration about forty cubic inches of air are received into the lungs, and at each expiration the same quantity is discharged. If, therefore, we calculate that twenty respirations take place in a minute, and forty cubic inches to be the amount of each inspiration, it follows, that in one minute, we inhale 800 cubic inches; in an hour, the quantity of air inspired will be 48,000 cubic inches; and in the twenty-four hours, it will amount to 1,152,000 cubic inches. This quantity of air will almost fill 78 wine hogsheads, and would weigh nearly 53 pounds. From this admirable provision of nature, by which the blood is made to pass in review, as it were, of this immense quantity of air, and over so extensive a surface, it seems obvious, that these two fluids are destined to exert some very important influence on each other; and it has been proved, by a very decisive experiment of Dr. Priestley's, that the extremely thin membrane, which is alone interposed, does not prevent the exercise of the chemical affinity which prevails between the air which is received in the lungs, and the blood which is incessantly circulating through them. It must surely, therefore, be of the first importance to health, that the fluid of which we hourly inhale, at least, three hogsheads, should not be contaminated by the suspension of noxious effluvia.

The purity of the atmosphere may be impaired either by the operation of what some denominate natural causes, or by the influence of circumstances resulting from our social condition. Its chemical constitution is changed by respiration; the vital principle is destroyed, and its place supplied by a highly poisonous gas.

The emanations from the surface of our bodies contribute, in a still greater degree, to vitiate the atmosphere, and to render it less fit for the healthful support of life. Many of the organs which compose our wonderfully complicated frame are engaged in discharging the constituent parts of our bodies, which, by the exercise of the various animal functions, are become useless, and, if retained, would become noxious. Physiologists have instituted a variety of experiments, to ascertain the amount of the exhalations from the surface of the body. Sanctorius, an eminent Italian physician, from a series of experiments performed during a period of thirty years, estimates it as greater than the aggregate of all our other discharges. From his calculations it would appear, that if we take of liquid and solid food eight pounds in the twenty-four hours, that five pounds are discharged by perspiration alone, within that period; and of this, the greater part is what has been denominated insensible perspiration, from its not being cognizable to the senses. We may estimate the discharge from the surface of the body, by sensible and insensible perspiration, as from half an ounce to four ounces per hour.

The exhalations from the lungs and the skin are, to a certain extent, offensive even in the most healthy individuals; but when proceeding from those labouring under disease, they are in a state very little removed from putrefaction.

Animal miasmata, like all other poison, become more active in proportion to the quantity which we imbibe. When, therefore, the air is stagnant, and when many individuals contribute their respective supplies of effluvia to vitiate it, the atmosphere necessarily becomes satured with the poison; and when inhaled, conveys it in a more virulent and concentrated state to the extensive and delicate surface of the lungs.

The collection of animal effluvia in confined places, is the source of the generation and diffusion of febrile infection: but when the miasmata are respired, in a diluted state, the ill effects which they produce, though slower in their operation, are equally certain. They, to a certain extent, pollute the fountain of life, and ultimately break down the vigour of the most robust frame; impairing the action of the digestive organs, engendering the whole train of nervous disorders, and rendering the body more susceptible of disease.

The lungs and the skin may equally become the means of introducing poisonous or infectious matter into the constitution. The venom of a poisonous animal, the matter of small-pox, and many other contagions, produce their influence through the medium of the skin. Infectious diseases are communicated by the reception of air in our lungs, impregnated with contagious matter. The influence of the constant respiration of air in any degree impure, is fully evinced in the pallid countenances and languid frames of those who live in confined and ill-ventilated places; and the health of all classes of society suffers precisely in proportion to the susceptibility of their constitutions, and according to the greater or less impurities of the air which they habitually respire.

Of the offensive nature of animal effluvia, the senses of every one who enters a crowded assembly, must immediately convince him. When, therefore, we reflect on the state of the air which we breathe in churches, theatres, schools, and all crowded assemblies; and when we consider the amount of the exhalations emitted by each individual, and the very offensive nature of those emitted by many; and when, on the other hand, we take into consideration the importance of air to life, and the great quantity of this fluid which we daily respire, we must be naturally led to the adoption of such measures as would secure in our private dwellings, as well as in our public buildings, a full and unintermitting supply of fresh atmospheric air.

It is curious to observe the influence of habit, in reconciling us to many practices which would otherwise be considered in the highest degree offensive. Thus, while, with a fastidious delicacy, we avoid drinking from a cup which has been already pressed to the lips of our friends, we feel no hesitation in receiving into our lungs an atmosphere contaminated by the breath and exhalations of every promiscuous assembly.

"Were once the energy of air deny'd, The heart would cease to pour its purple tide The purple tide forget its wonted play, Nor back again pursue its curious way."

The next Subject of Curiosity we shall consider, is, THE HAIR OF THE HEAD.

If we consider the curious structure, and different uses of the hair of our heads, we shall find them very well worth our attention, and discover in them proofs of the wisdom and power of God.

In each entire hair we perceive with the naked eye, an oblong slender filament, and a bulb at the extremity thicker and more transparent than the rest of the hair. The filament forms the body of the hair, and the bulb the root. The large hairs have their root, and even part of the filament, enclosed in a small membraneous vessel or capsule. The size of this sheath is proportionate to the size of the root, being always rather larger, that the root may not be too much confined, and that some space may remain between it and the capsule. The root or bulb has two parts, the one external, the other internal. The external is a pellicle composed of small laminæ; the internal is a glutinous fluid, in which some fibres are united; it is the marrow of the root. From the external part of the bulb proceed five, and sometimes, though rarely, six small white threads, very delicate and transparent, and often twice as long as the root. Besides these threads, small knots are seen rising in different places; they are viscous, and easily dissolved by heat. From the interior part of the bulb proceeds the body of the hair, composed of three parts; the external sheath, the interior tubes, and the marrow.

When the hair has arrived at the pore of the skin through which it is to pass, it is strongly enveloped by the pellicle of the root, which forms here a very small tube. The hair then pushes the cuticle before it, and makes of it an external sheath, which defends it at the time when it is still very soft. The rest of the covering of the hair, is a peculiar substance, and particularly transparent at the point. In a young hair this sheath is very soft, but in time becomes so hard and elastic, that it springs back with some noise when it is cut. It preserves the hair a long time. Immediately beneath the sheath are several small fibres, which extend themselves along the hair from the root to the extremity. These are united amongst themselves, and with the sheath that is common to them, by several elastic threads; and these bundles of fibres form together a tube filled with two substances; the one fluid, the other solid; and these constitute the marrow of the hair.

The wonders of creating power are seen in every thing, even in the hair that adorns our surface.